Reported in the December 11 issue of Science, an analysis of Tawa hallae, a meat-eating theropod dinosaur between two-and-four meters long, reveals that the early history of theropods was characterized by waves of migration from South America, not just localized or regional species diversification.
“To understand how these early theropods were related evolutionarily, we analyzed hundreds of morphological features then used recently devised statistical methods to model how the distributions of these dinosaurs evolved during the Triassic,” says Alan H. Turner, Ph.D., Assistant Professor of Anatomical Sciences at Stony Brook University and a co-author of the study.
Originally excavated in 2006 at Ghost Ranch in northern New Mexico, two nearly complete skeletons and several other partial specimens of Tawa hallae provided the scientists with the samples they needed to complete a full anatomical analysis and model its evolutionary history. This anatomical information gathered from Tawa helped fit all Triassic theropod dinosaurs into the evolutionary tree of the group.
At Ghost Ranch, Dr. Turner and colleagues observed three distantly related carnivores in the Late Triassic beds, which implied that each carnivore descended from a separate lineage before arriving in North America, instead of all three evolving from one local ancestor. The skeletons of Tawa found in that area display characteristics that exist in the two others excavated at Ghost Ranch, fossils from a carnivore closely related to Herrerasaurus, which lived in South America, and Coelophysis, common to North America. Yet, Tawa also had features of neither, which indicates a separate lineage.
Tawa is an example of a fossil that fills a morphological gap, which arises when a fossil record is incomplete. The researchers point out that the fossil is not a missing link on the dinosaur evolutionary chain, as it evolved on its own lineage. In addition, because Tawa was well preserved and a complete skeleton, the team was able to answer a lot of questions that normally surface when examining fossil lineage.
“One of the biggest morphological gaps in early dinosaurs lies between Herrerasaurus and animals that are clearly more related to birds, such as Coelophysis or Dilophosaurus,” explains Sterling Nesbitt of the University of Texas at Austin, the lead author of the study. “Tawa fits perfectly in between, morphologically. It retains characteristics that existed in Herrerasaurus that we thought were more primitive while also possessing features seen in unmistakable theropods (including birds), such as the presense of air sacs surrounding the braincase and neck.”
Dr. Turner, an expert on theropod dinosaur evolution and biogeography, the study of how and where organisms distribute around the world, explains that in the Triassic when Tawa and animals like them were evolving all the continents were united in a single landmass called Pangaea. However, by the Late Triassic North America was becoming isolated from present day continents (i.e., South America, Europe). Isolation is an important aspect of the speciation process, and thus evolution.
“Based on this, we had predicted that the theropod dinosaurs we were finding in North America at Ghost Ranch would form their own group, or clade, separate from their South American cousins. What we found from the data was the opposite,” says Turner.
“The North American dinosaurs did not form an endemic group. We discovered that their closest relatives lived in South America, not North America. This indicates that long range dispersal was prevalent at the time.”
Dr. Turner says that the team’s anatomical analysis, combined with biogeographic tests detailed in the study demonstrate that Triassic carnivorous dinosaurs from the quarry dispersed multiple times into North America. Dispersal of early dinosaurs it seems was prevalent during the Triassic, suggesting that the lack of sauropodomorph (long-necked) dinosaurs in North American was not a result of physical barriers.
“We don’t know why sauropodomorphs were not in North America, but it looks increasingly likely that they were getting here but something was preventing them from staying,” says Turner.
“Many questions remain but discoveries like Tawa are allowing us to evaluate these questions in ways we were not able to in the past.”
In addition to Turner and Nesbitt, authors include Nathan Smith of the University of Chicago and the Field Museum of Natural History; Randall Irmis of the Utah Museum of Natural History and the University of Utah; Alex Downs of the Ruth Hall Museum of Paleontology in New Mexico, and Mark Norell of the American Museum of Natural History.
The research for the study was supported by the National Science Foundation (NSF) through grants to individual researchers, as well as the National Geographic Society, the University of Chicago, the Field Museum of Natural History, the University of Utah, the Ruth Hall Museum of Paleontology, and Stony Brook University. To read more about Tawa, visit http://www.nsf.gov/news/special_reports/tawa/.
The Department of Anatomical Sciences is one of 25 departments within Stony Brook University School of Medicine. Fields of study include research on human evolutionary anatomy, morphology and vertebrate paleontology.
Greg Filiano | Newswise Science News
Receding glaciers in Bolivia leave communities at risk
20.10.2016 | European Geosciences Union
UM researchers study vast carbon residue of ocean life
19.10.2016 | University of Miami Rosenstiel School of Marine & Atmospheric Science
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Life Sciences
21.10.2016 | Life Sciences
21.10.2016 | Life Sciences